Justin Welby says Christians need the “protection and encouragement of governments” as populations in some countries plummet.
Christian communities in the Middle East face the prospect of “imminent extinction”, the Archbishop of Canterbury has warned.
“Many have been killed, enslaved and persecuted or forcibly converted,” he wrote in the Sunday Telegraph.
Justin Welby said hundreds of thousands had been “forced from their homes”.
Looking at individual countries, the archbishop said the Christian population of Iraq was less than half what it was in 2003, while Christians’ “churches, houses and businesses have been damaged or destroyed”.
He added: “The Syrian Christian population has halved since 2010.
“As a result, across the region Christian communities that were the foundation of the universal Church now face the threat of imminent extinction.”
Tensions in the region can make make life difficult even for Christians who are physically secure in “democratic states such as Israel”, he wrote.
He also warned against looking for “obvious solutions”.
He explained: “To ask Syrian Christians to choose between President Assad, under whom they were tolerated, and the unimaginable horrors and threats of so-called Islamic State, is to impose a choice that we would not accept for ourselves, and which we should not judge too easily.”
Those that wish to leave should be considered “refugees in need of asylum”, he said.
The archbishop said there would be a service at Westminster Abbey on Tuesday, at which Prince Charles will play a “leading role”.
“We will celebrate and pray for Christians in the region, we will raise their profile and we will publicise their plight,” he said.